The upcoming new president of the United States has a huge job to do to reverse what many see as the bad influence the US has had on world-wide environmental policy.

As he assumes the presidency, Barack Obama must make climate-change legislation and investment in green energy top priorities. And he must be ready to take bold — and politically unpopular — action to address global warming.

And so our eight-year interlude from reality draws to a close, and the job of cleaning up begins. The trouble is, we're not just cleaning up after a failed presidency. We're cleaning up after a two-century binge.

Barack Obama won an historic victory yesterday, and with it the right to take office under the most difficult circumstances since Franklin D. Roosevelt. Maybe more difficult, because while both FDR and Obama had financial meltdowns to deal with, Obama also faces the meltdown meltdown — the rapid disintegration of the planet's climate system that threatens to challenge the very foundations of our civilization.

Do you think that sounds melodramatic? Let me give it to you from the abstract of a scientific paper written earlier this year by one of the people who now work for Mr. Obama, NASA scientist James Hansen. "If humanity wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted, paleo-climate evidence and ongoing climate change suggest that CO2 [in the atmosphere] will need to be reduced from its current 385 ppm [parts per million] to at most 350 ppm." In other words, if we keep increasing carbon any longer, the earth itself will make our efforts moot.

Hansen's calculation is a scientifically grounded way of saying: Everything must change at once. To meet his target,before enough feedback loops kick in to irrevocably warm the planet, Hansen says fossil-fuel combustion, particularly coal, must cease around the planet by about 2030, and that it must happen sooner in the industrialized nations. As the climate observer, and tireless blogger, Joe Romm observed when Hansen's paper was published, it means that "we need to go straight to the government-led WWII-style effort for the whole planet that is sustained for decades." (Well, back to FDR, what do you know).

Anyway, here are some of the pieces of what Obama must push for:

Massive government investment in green energy. For this to have any hope of being politically viable, it will need to be seen as the single huge stimulus effort that might lift us out of our financial swamp. (That's almost certainly true, by the way — name another emergent technology capable of re-floating the economy for the long run). We have at least some of the technologies we'd need — wind, the newly promising desert solar arrays, and the ever-useful insulation (the installation of which would at least create a lot of jobs — you're not going to send your house to China for a layer of fiberglass). You might also push for nuclear, but it takes a long time and it's probably too expensive to make a rational list. Still, no holds barred.

A stiff cap on carbon, which will help drive the process. Again, to have any chance of passing politically, it will need to come with the feature proposed in recent years by Peter Barnes, and that Obama has semi-endorsed: a "cap and share" approach that would return the revenue raised directly to consumers. That is, Exxon would pay for the permit to pour carbon into the atmosphere, a cost that would rise steadily as the cap was lowered. But instead of the money going into government coffers, every American would get a check each year for their share of the proceeds. They'd be made whole against the rising cost of energy, while the shock that the price signal would send would be preserved. Current versions of cap-and-trade are too weak and too riddled with loopholes — getting a clean, tough bill through Congress needs to be a preoccupation of President Obama.

Once the president has done all that tough stuff at home, he'll need to do it all over again, globally. The world is meeting in Copenhagen in December of 2009 to come up with a successor to the Kyoto treaty, the modest first international effort that George W. Bush walked away from weeks after taking office. If Hansen and others are even close to right, this will represent the last legitimate shot the world has at putting itself on a new carbon regime in time to make any difference.

It will be incredibly difficult, mostly because we begin from such unequal places. China has lots of coal and it would like to burn it, because it's the cheapest way to pull rural Chinese out of dire poverty (something the country's leaders would quite like to do because otherwise they won't be the country's leaders much longer). If we want them to use, say, windmills instead, we're going to need to "share some wealth," north to south, to make it happen. The Chinese opened the bidding last week, with a suggestion that one percent of the U.S. annual GDP would be a good amount to send their way. That's going to be quite a political ask — it means that Americans would be working roughly one hour every two weeks just to help the global South build up their clean alternatives. What we're talking about is a carbon version of the Marshall Plan, and it would mean Obama needs to be not just FDR but Truman and Ike as well.

What it all boils down to is: The bills are coming due. And not just, or even mainly, the bills from a failed Bush presidency,but the bills from 200 years of burning fossil fuel. Twenty years ago when we started worrying about global warming, we thought we'd have a generation to pay those bills off. But we were wrong — the planet was more finely balanced than we'd realized. The melting Arctic is the call from the repo man.

Any hope of succeeding will require Obama to grasp, deep in his guts, the fact that climate, energy, food, and the economy are now hopelessly intertwined, and that trying to solve any one of these problems without taking on the others simply makes all of them worse. More, he needs to understand, again viscerally, the single stark fact of our time: No matter how many votes, no matter how much lobbying, no matter how much pressure you apply, you can't amend the laws of physics and chemistry. They aren't like the laws that politicians are used to dealing with. They will be obeyed, like it or not. 350 is now the most important number on the planet, the red line that defines reality reality.

It doesn't define political reality, however. The political reality goes like this: George W. Bush was so terrible on this issue that the bar has been set incredibly low — Obama will get all the political points he needs with fairly minimal effort. Doing what actually needs to be done will be politically unpopular isn't even the word. It might well wreck his political future, because it would involve — directly or indirectly — raising the cost of continuing to live as we do right now.

My guess, from the outside, is that all Obama's instincts are centrist. Certainly in energy policy he's offered nothing all that bold or interesting, though his sophistication and engagement have grown during the campaign, which is a good sign. A better sign is simply that, by every testimony, he's one of the smartest men ever to assume high political office in this country. Not just smarter than Bush. Really smart. Smart enough, if he sits down to really understand the scale of the problem he faces, that he might decide to take the gambles that the situation requires. He said, not long ago, "under my plan of a cap-and-trade system, electricity rates would necessarily skyrocket" — which is a sign of someone who is aware there may be a reality to come to grips with.

First signs to watch for: Does he go to Poland next month for the United Nations Climate Change Conference, and in so doing electrify the international talks over carbon? Are people like green-jobs advocate Van Jones on the short list of those he's listening to on energy policy? Can he see clear to making this — after dealing with the short-term financial emergency — his first legislative priority, even before health care?

Obama, and the rest of us, have a lot more to fear than fear itself. We've got carbon, and right now that's the most frightening stuff on earth.

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